With development of wireless technologies, a device-to-device D2D) communication technology is proposed to relieve network load. User equipments (UEt) within a particular distance range may directly communicate with each other by using the D2D communication technology (D2D technology for short), and a third-party device such as a base station does not need to be used for relaying. As shown in FIG. 1, in coverage of a base station, the base station may separately communicate with UE 1, UE 2, and UE 3 by using a cellular link. After the D2D technology is used, the UE 1 can directly communicate with the UE 2 or the UE 3 by using a D2D communications link (also referred to as a slide link, SL for short), the UE 2 can directly communicate with the UE 1 or the UE 3 by using the SL, and the UE 3 can communicate with the UE 1 or the UE 2 by using the SL.
In the D2D technology, an idea that user equipment is used as a relay node is proposed to improve a network communication capability. However, how to improve communication reliability of a network using the D2D technology is an urgent problem to be resolved.